Opponents of identity cards yesterday stepped up their campaign for the multi-billion pound scheme to be scrapped, after it emerged that the government is planning a scaled-down version of the project so that it can meet a 2008 deadline.

The plans emerged in a series of emails between officials working on the project, leaked to the Sunday Times, which warn that the interim version may not be "even remotely feasible". One of the civil servants involved warned that a botched introduction could delay ID cards for a generation. He added: "This has all the inauspicious signs of a project continuing to be driven by an arbitrary end date, rather than reality."

David Davis, the shadow home secretary, warned: "These are all the classic signs of a Whitehall IT project about to go disastrously wrong. These civil servants can see plainly what the government refuses to accept. The prime minister's obsession with this project will actually weaken our security and cost at least £20bn. It's time they admitted failure and cancelled this project."

Nick Clegg, the Liberal Democrats' home affairs spokesman, said the government was in denial about the scheme.

A Home Office spokesman conceded that the government was considering an "early variant" on ID cards, allowing it to meet its pledge to phase in the cards from 2008. But he added: "Any suggestion we have abandoned [ID cards'] introduction is simply wrong."

In one email, David Foord, the director in charge of identity and defence at the Office of Government Finance, which audits projects for the Treasury, warned: "We are setting ourselves up to fail. Even if everything went perfectly (which it will not) it is very debatable whether whatever TNIR [the temporary scheme] turns out to be ... can be procured, delivered, tested and rolled out in just over two years."

Peter Smith, the acting commercial director at the new Identity and Passport Service, said the Home Office agency was seeking to ensure contracts would work "even if the ID card gets canned completely".

Mr Foord responded: "I do not have a problem with ministers wanting a face-saving solution. [But] a botched introduction of an early variant ID card ... if it is subject to a media feeding frenzy, which it might well be close to a general election, could put back the introduction of ID cards for a generation."

Researchers at the London School of Economics said the emails indicated a meltdown in the planning and execution of the project, vindicating their predictions, which had been repeatedly criticised by ministers.

More than 100 senior academics, independent experts and industry specialists contributed to the LSE's Identity Project, which concluded that the government's proposals would be "too costly, technically risky and complex". Yesterday they called for the Treasury and the Department for Trade and Industry to take over the scheme, as the Home Office was incapable of managing it.

They urged the government to launch a National Audit Office inquiry into how up to £70m had been spent planning the scheme.

Simon Davies, the project's co-mentor, said: "Everything we warned could happen, has happened. If government wants to rescue this scheme from certain oblivion it must take action swiftly to restore the fragments of remaining trust."